Revert "only add message listener when we're adding a new channel"

This reverts commit 1dbd522.

It seems this commit introduced a regression in functionality such that
messages do not appear in channels
(#78) and might also be
responsible for a similar bug in cabal-desktop@6.0.8

It would be good to only add the relevant message listeners, instead of
duplicates, but I think it will have to be done anew with fresh eyes.

src/cabal-details.js

@@ -800,9 +800,10 @@ class CabalDetails extends EventEmitter {
       const details = this.channels[channel]
       if (!details) {
         this.channels[channel] = new ChannelDetails(cabal, channel)
-        // note: only add listener if we don't have a channel registered (=> prevent duplicate listeners)
-        cabal.messages.events.on(channel, this.messageListener.bind(this))
       }
+      // TODO: only do this for our joined channels, instead of all channels
+      // Calls fn with every new message that arrives in channel.
+      cabal.messages.events.on(channel, this.messageListener.bind(this))
       this._emitUpdate('new-channel', { channel })
     })
   }

src/initialization-callbacks.js

@@ -14,14 +14,13 @@ module.exports.getArchivesCallback = function (err, archivedChannels) {
       const details = this.channels[channel]
       if (!details) {
         this.channels[channel] = new ChannelDetails(cabal, channel)
-        // listen for updates that happen within the channel
-        // note: only add listener if we don't have a channel registered (=> prevent duplicate listeners)
-        cabal.messages.events.on(channel, this.messageListener.bind(this))
       }
       // mark archived channels as such
       if (archivedChannels.indexOf(channel) >= 0) {
         this.channels[channel].archive()
       }
+      // listen for updates that happen within the channel
+      cabal.messages.events.on(channel, this.messageListener.bind(this))
 
       // add all users joined to a channel
       cabal.memberships.getUsers(channel, (err, users) => {